The present invention relates to boosters incorporated in brake apparatus for automobiles and other vehicles. More particularly, the present invention relates to an electric motor-driven booster using an electric motor as a boost source.
A publicly known electric motor-driven booster is disclosed, for example, in Japanese Patent Application Publication No. 2008-30599. The electric motor-driven booster has an input rod connected to a brake pedal, a pressing member pressing a piston in a master cylinder, an electric motor driving a booster piston through a rotation-rectilinear motion conversion mechanism, a stroke simulator giving a predetermined reaction force to the input rod, and a controller controlling the operation of the electric motor according to the movement of the input rod. With this structure, the controller controls the operation of the electric motor to propel the piston in the master cylinder through the pressing member according to the amount of operation of the brake pedal, thereby generating a brake fluid pressure to obtain a desired braking force.
In addition, the controller appropriately adjusts the output of the electric motor in accordance with the amount of operation of the brake pedal, thereby enabling the so-called boost ratio to be varied. Thus, it is possible to execute various brake control operations, such as boost control, brake assist control, regenerative cooperative control, and so forth. In this regard, the vehicle driver does not feel uncomfortable even when the output of the electric motor is changed by regenerative cooperative control or the like because the stroke simulator gives a predetermined reaction force to the brake pedal in response to the brake pedal depression.
If the electric motor should become unable to operate due to a failure in the electric system or the like, the pressing member can be pressed directly by the input rod connected to the brake pedal to propel the piston in the master cylinder, thereby enabling the braking function to be maintained.